EP1179441B1 - Tyre with asymmetric belt structure and method of mounting said tyre on a vehicle - Google Patents

Abstract

A tire has stiffening layer (8) lying between radial carcass (2) and a multi-layer crown (3). The stiffening layer is only on one side of the equatorial plane. The tire has marks to indicate the side having the stiffening layer so the tire is correctly mounted on a wheel. Each layer has parallel cables or filaments. The cables in adjacent layers of the crown are crossed. The cables in the stiffening layer are at 50 - 90 degrees to the circumferential direction. Independent claims are included for the following: (a) Non-symmetrical tires as above for a vehicle. The stiffening layer is 15-45% of the width of the crown and its furthest edge is at 35-50% of the crown width from the equatorial plane. (b) Mounting a set of tires as in (a) to a vehicle. (c) Modification of (b) omitting the 35-50% limit. Preferred Features: The stiffening layer is 20-35% of the width of the crown. The metallic cables or filaments in the stiffening layer have a combined average stiffness ≥ 1GPa. The crown has textile cables. The angle of the cables in the stiffening layer and the adjacent layer of the crown are the same.

Description

The invention relates to tires with radial carcass and reinforced crown under the tread by means of superposed plies of threads or cables constituting, in the following description, the crown reinforcement. It also relates to a method of mounting a tire train on a road vehicle.

A tire for a passenger vehicle generally comprises a radial carcass reinforcement anchored in two beads and radially surmounted by a crown reinforcement itself surmounted radially by a tread intended to come into contact with the roadway during driving. The crown reinforcement comprises at least two sheets, said working, each sheet being composed of a plurality of son or cables substantially parallel to each other in the same sheet, the son or cables of a sheet being crossed with the yarns or webs of the adjacent web (s).

To improve the general characteristics of the rolling behavior of a vehicle equipped with tires, it is known to employ tires having structural asymmetries.

The document FR 1.342.822, for solving a problem of wear on a vehicle traveling on a trajectory with relatively small radii of curvature, teaches forming an asymmetric vertex reinforcement by providing that the transverse rigidity of the tread decreases by one. edge to the other and in that the least rigid portion is turned towards the outside of the vehicle when said tire is mounted on said vehicle. To obtain this dissymmetry, it is proposed, among the examples described, to form a crown reinforcement to a ply extending over the entire width of the tread and a second ply on only a part of said width so as to give said band has greater transverse stiffness on one side than the other.

The presence of rigidity dissymmetry in a tire, although interesting in terms of the performance of vehicle running behavior, is not without a number of drawbacks and in particular that of drifting when said vehicle travels in a straight line (ie a distribution of forces on the tread substantially equivalent to what occurs in cornering). It follows penalizing contact solicitations from a point of view of the tread of the tire; the forces exerted by the roadway on the tires of the vehicle further causes a lateral draw of the vehicle, that is to say that it gradually deviates from its path during a taxi in a straight line.

To treat this problem, the document FR 1.444.271 proposes a means for attenuating the effects of a dissymmetrical structure while traveling in a straight line by superimposing on said structure a second asymmetry in order to counterbalance the effects of the first dissymmetry while maintaining the good performance in cornering behavior obtained for example thanks to the presence of the first asymmetry. The examples cited lead either to the addition of an additional reinforcing element (carcass ply extending under the crown reinforcement) or to an excess thickness of the tread located on only part of said strip.

The objective of the invention is to provide a high-performance asymmetric tire structure in cornering and in a straight line which substantially reduces the lateral draft of a vehicle equipped with this type of tire and thereby avoids the appearance of irregular wear. linked for example to drifting during a taxi in a straight line. The applicant has found that by the choice of particular values of a certain number of parameters it is possible to obtain a substantial improvement in performance while maintaining a certain dissymmetry of the structure of the tire without making the tire heavier.

The objective is achieved with a tire having a preferred direction of assembly on a road vehicle and comprising two beads, a top and two flanks ensuring the connection between the beads and the crown, this tire having a carcass reinforcement extending from one bead to the other and, radially on the outside, a crown reinforcement, of width Ls, formed by a stack of at least two crown plies, each of these plies having a width greater than or equal to Ls. and comprising a plurality of son or cables arranged in parallel in substantially the same direction, the cables being crossed from one sheet to the next.

This tire further comprises a meridian stiffening ply disposed radially between the carcass reinforcement and the crown reinforcement and comprising a plurality of wires or cables substantially parallel to each other and forming with the circumferential direction an average angle of between 50.degree. ° and 90 °; this ply of width Lr measured between a first end and a second end, has its two ends located on the same side with respect to the equatorial plane of the tire.

This tire is characterized in that it comprises locating means for indicating the side of the tire on which the meridian stiffening ply is located, these locating means serving to position said ply on the inside of a vehicle when this tire is mounted on said road vehicle.

The width Ls of the crown reinforcement is taken as the smallest of the widths of the summit plies; it corresponds to the effective width of the armature, that is to say the width on which there is a mechanical coupling between the crown plies.

If the state of the prior art discloses tires having vertices comprising so-called triangulation plies and arranged symmetrically with respect to the equatorial plane of said tires, the invention proposes a new and non-obvious solution consisting in the combination of presence of a single meridian stiffening ply with the indication of the necessary position of this ply with respect to a vehicle, once the tire mounted on said vehicle which achieves good performance in driving in a straight line and cornering without negative effects in wear and lateral draw.

US-A-3,254,693 discloses a tire whose crown reinforcement structure comprises at least one ply having a discontinuity and addresses the problem that it has been found that this type of tire functions in the manner of two tires. This document shows a structure comprising two meridian stiffening plies, a ply on each side of the equatorial plane and does not describe any asymmetrical arrangement.

Various locating means may be employed (such as those used in US-A-3,435,874 describing the use of locating means on a tire having taper forces), including marking on one of the sidewalls of the tire. identifying the side where the meridian stiffening ply is located, a specific marking on the external or internal surface of the tire indicating the side of the tire to be placed outside or inside the vehicle knowing that the meridian stiffening ply is located on the inside.

• la largeur Lr de la nappe de rigidification méridienne est comprise entre 15 et 45 % de Ls;
• la première extrémité de cette nappe de rigidification méridienne est située à une distance D1 du plan équatorial du pneumatique comprise entre 35 % et 50 % de Ls, la seconde extrémité de la nappe de rigidification méridienne étant située entre la première extrémité et le plan équatorial du pneumatique ;
• la rigidité moyenne de compression de la nappe de rigidification méridienne dans le sens des fils ou câbles de ladite nappe, est supérieure à 1 Gpa, cette rigidité étant obtenue en multipliant la rigidité de compression d'un seul fil ou câble par le nombre de fils ou câbles par unité de longueur de nappe.

With the tire according to the invention, the following characteristics can also be used alone or in combination:

• the width Lr of the meridian stiffening ply is between 15 and 45% of Ls;
• the first end of this meridian stiffening ply is situated at a distance D1 from the equatorial plane of the tire of between 35% and 50% of Ls, the second end of the meridian stiffening ply being situated between the first end and the equatorial plane of the tire. pneumatic;
• the average stiffness of the meridian stiffening ply in the direction of the son or cables of said ply is greater than 1 Gpa, this rigidity being obtained by multiplying the compression stiffness of a single wire or cable by the number of wires or cables per unit length of web.

The combination of the above-mentioned parameters makes it possible to benefit from the advantages of an asymmetric tire architecture, while not requiring the presence of additional means to counterbalance the effects of the drift induced during driving in a straight line. The interest of a tire according to the invention is significant since the phenomena of irregular wear in running straight line (in the sense of localized wear on certain areas of the tread) are substantially attenuated.

When Lr is less than 15% of Ls, the stiffening effect of the additional meridian stiffening layer is insufficient to measure the effects on the tire; when Lr is greater than 45% of Ls, it occurs, when the tire is subjected to a high rotational speed, induced effects that can penalize the running performance of said tire.

Similarly, in order to avoid blocking in the radial direction of the median portion of the tire vertex rotated about its axis, it is preferable to provide that the second end of the meridian stiffening ply is located with respect to the equatorial plane at a distance D2 greater than one-third of Lr.

When a tire according to the invention is rotated at a high rotational speed, the presence of a meridian stiffening ply has an effect by its only additional mass compared to the same tire without this ply. To minimize this effect, it is preferable to provide that the end of the meridian stiffening sheet farthest from the equatorial plane is located at a distance D1 of said plane between 35% and 45% of the total width Ls of the crown frame.

To achieve a substantial lightening of the crown reinforcement and therefore of the tire, it is advantageous to provide that the crown reinforcement is constituted by at least two crown plies, each crown ply being composed of a rubber matrix reinforced by a plurality of textile threads or yarns arranged in parallel in substantially the same direction, the crown stiffening ply being reinforced by metal threads or cords. This arrangement makes it possible to confer on the crown reinforcement a level of rigidity in bending on satisfactory edge; it also makes it possible to reduce substantially the rolling resistance of a tire comprising this crown reinforcement. The same positive effects are achieved if rubber mixtures of low modulus of elasticity are used in combination, said mixtures coating the textile cables of the working plies.

Preferably, the gum mixture of the plies of the crown reinforcement and the meridian stiffening ply has an extension modulus, at 10% deformation and at ambient temperature, of less than 12 MPa and a loss at 60 ° C. less than 25%.

Advantageously, the width Lr of the additional stiffening ply of substantially meridian orientation is between 20 and 35% of the effective width of the crown reinforcement comprising all the so-called working plies.

An optimum effect is achieved when the average angle made by the reinforcements (in the form of son or cables) of the additional meridian stiffening ply is between 70 ° and 90 °; this angle being measured with respect to the equatorial plane perpendicular to the axis of rotation of the tire and passing through the middle of the width of the crown reinforcement.

In addition, a rubber profile having a thickness between 0.3 and 1 mm (thickness measured radially above the axially outermost end of the stiffening ply) and an extension module with 10% deformation, measured under standard test conditions and at ambient temperature, of at least 5 MPa and at most 15 MPa, this section extending in a manner continuous in the circumferential direction and having, seen in a radial sectional plane (ie containing the axis of rotation of the tire), its axially innermost end located at a distance from the lower equatorial plane at the distance from the axially outermost end of the stiffening ply measured with respect to the same equatorial plane.

It is moreover interesting to associate with the tire according to the invention the presence of a tread sculpture, half of this band located radially outside the additional meridian stiffening sheet being provided with a clean tread pattern. formed of relief elements, this sculpture having a sculptural rigidity lower than the sculptural rigidity of the other half of the tread; in this case, the thicknesses of the tread are substantially constant over the entire width of said strip. Tread rigidity essentially means the rigidity of the tread when the tire according to the invention, under normal conditions of use (inflation pressure and load supported), is biased drift.

Furthermore, it is proposed a method of mounting a set of four pneumatic asymmetric structure allowing improved performance of cornering while allowing a reduction of tire wear and lateral draw on vehicle, each tire having two beads, a top and two flanks providing the connection between the beads and the top, each tire having a carcass reinforcement extending from one bead to the other and, radially outwardly, a crown reinforcement, width equal to Ls, formed by a stack of at least two crown plies, each of these crest plies having a width greater than or equal to Ls being composed of a plurality of son or cables arranged in parallel in substantially the same direction; cables being crossed from one sheet to its next.

Each tire further comprises a meridian stiffening ply disposed radially between the carcass reinforcement and the crown reinforcement and formed by a plurality of wires or cables substantially parallel to each other and forming a medium angle with the direction circumferential between 50 ° and 90 °, this web width Lr being entirely located on the same side with respect to the equatorial plane of the tire.

The method according to the invention consists in mounting four tires as described so that the meridian stiffening sheet of each tire mounted on the vehicle is located on the vehicle interior side, that is to say between the inside of the vehicle. vehicle and the equatorial plane of the tire.

By definition, the equatorial plane is the plane perpendicular to the axis of rotation of the tire passing through the middle of the crown reinforcement.

Preferably, the width Lr, measured between a first end and a second end is between 15 and 45% of Ls, the first end of this meridian stiffening sheet being located at a distance D1 of the equatorial plane of the tire of between 35% and 50% of Ls, the second end of the meridian stiffening sheet being located between the first end and the equatorial plane of the tire.

For each tire, the average stiffness of the meridian stiffening ply in the direction of the yarns or cables of said ply is preferably greater than 1 Gpa, this rigidity being obtained by multiplying the compression stiffness of a single wire or cable. by the number of wires or cables per unit length of web.

The proposed method, according to which the meridian stiffening plies of the four tires of a vehicle are positioned towards the interior of the vehicle, also applies to the fitting of the tires of the front axle of said vehicle, but does not, however, make it possible to achieve the same level of performance result for the vehicle.

• la figure 1 montre une coupe méridienne d'un pneumatique selon l'invention comportant une nappe supplémentaire de rigidification méridienne;
• la figure 2 montre en vue éclatée l'orientation des câbles des différentes nappes;
• la figure 3 montre les rigidités de dérive calculées pour le pneumatique présenté avec la figure 1 comparées aux rigidités de dérive calculées pour le même pneumatique sans nappe de rigidification méridienne.

A nonlimiting example of practical realization is presented below with the attached drawings according to which:

• Figure 1 shows a meridian section of a tire according to the invention comprising an additional meridian stiffening ply;
• Figure 2 shows in exploded view the orientation of the cables of the different layers;
• FIG. 3 shows the calculated drift stiffnesses for the tire presented with FIG. 1 compared to the drift stiffnesses calculated for the same tire without meridian stiffening ply.

In FIG. 1, showing a meridian section of a passenger tire 1 of dimension 195/65 R 15, there are two beads 12 extended by sidewalls 6 themselves connected to the two lateral ends of a tread 7. pneumatic 1 comprises a carcass reinforcement 2 extending from one bead to the other and anchored in each of said beads 12 by turning around an inextensible annular element 11. This carcass reinforcement 2, formed in the present case of a ply of radially oriented 144/2 PET cables (that is to say making an equatorial plane with an angle equal to or close to 90 °) is surmounted in its median region and radially outwards by a reinforcement of top 3 surmounted by a tread 31 for contact with the roadway during driving.

The crown reinforcement 3 of this tire is composed of a stack of first and second working plies 4, 5 each formed of a plurality of parallel cables, said cables being metal cables of formula 3 26 (three sons of 26/100); the angle of the cables of the first ply 4 forming with the circumferential direction an angle β 1 substantially equal to 25 ° and those of the second ply 5 making an angle β 2 substantially equal to 25 ° (these angles are clearly visible in the figure 2). In the case presented, the first working ply 4 is located radially between the carcass ply 2 and the second working ply 5 and has a width LI (measured between the ends 51 of this ply) greater than the width of the second ply . The effective width Ls of the crown reinforcement 3 in this example is defined as the width of the second working ply (measured between the ends 41 of this ply).

• largeur L1 : 160 mm; largeur efficace du sommet Ls : 146 mm ;
• largeur Lr = 40 mm (soit 27 % de Ls) ;
• distance D1, séparant la première extrémité de la nappe de rigidification méridienne 8 du plan équatorial, égale à 60 mm (soit 41% de Ls) ;
• distance D2, séparant la deuxième extrémité de la nappe de rigidification méridienne 8 du plan équatorial, égale à 20 mm
• angle des renforts de la nappe de rigidification méridienne 8 : 90° ;
• rigidité moyenne de compression dans le sens méridien de la nappe de rigidifcation méridienne 8 égale à 7 Gpa. Cette rigidité est obtenue en multipliant la rigidité de compression d'un câble par le nombre de câbles par unité de surface de ladite nappe. Le pas des câbles de la nappe de rigidification est égal à 2.0 mm.

In addition, there is arranged radially between the carcass ply 2 and the crown reinforcement 3 a meridian stiffening ply 8 formed of a plurality of metallic cables of formula 3-26 identical to those used in the working plies (this web is visible on the left side of the tire section shown in Figure 1, corresponding to the side of the tire intended to be placed on the side of the vehicle). This meridian stiffening ply 8 comprises, seen in section in FIG. 1, two ends, a first end 9 close to an edge of the crown reinforcement 3 and a second end 10 located between this first end 9 and the equatorial plane. whose trace is marked by XX ', and has the following characteristics:

• width L1: 160 mm; effective width of the apex Ls: 146 mm;
• width Lr = 40 mm (ie 27% of Ls);
• distance D1, separating the first end of the meridian stiffening ply 8 from the equatorial plane, equal to 60 mm (41% of Ls);
• distance D2, separating the second end of the meridian stiffening ply 8 from the equatorial plane, equal to 20 mm
• reinforcing angle of the meridian stiffening ply 8: 90 °;
• average stiffness of compression in the meridian direction of the meridian stiffening ply 8 equal to 7 Gpa. This rigidity is obtained by multiplying the compression stiffness of a cable by the number of cables per unit area of said web. The pitch of the cables of the stiffening ply is equal to 2.0 mm.

This tire thus described is intended to be mounted on a vehicle so that the flank located axially on the side of the meridian stiffening ply is placed towards the inside of the vehicle, the other sidewall being consequently oriented towards the outside of said vehicle. vehicle.

Among variations not shown, the first web may be narrower than the second web of work and in this case again the effective width Ls of the crown reinforcement is taken as the smallest of the widths of said webs. Another alternative structure of the crown reinforcement comprises a working ply whose at least one end is folded over itself the meridian stiffening ply may be preferably placed on the side where there is no folding.

FIG. 2 schematically shows the carcass reinforcement 2, the working plies 4, 5 composing the crown reinforcement 3 and the meridian stiffening ply 8 for the tire described with the support of FIG. 1. The references used on the two figures 1 and 2 have the same meanings. In this FIG. 2, the cables making up the first working ply 4 make an angle β 1 equal to 25 ° with respect to the equatorial plane whose trace in the plane of the figure is indicated by the line EE '; the cables of the second working ply 5 make an angle β 2 equal to 25 ° with respect to the equatorial plane. The steel cables of the stiffening ply 8 are at an angle α of 90 °.

In the case where the cables of the meridian stiffening ply form an angle α different from 90 ° with the equatorial plane, it is then preferable for said cables to have an orientation of the same sign as the angle of the reinforcements of the ply of the ply. crown reinforcement radially above said stiffening ply (this amounts to saying that the reinforcements of said plies have the same direction of inclination with respect to the equatorial plane).

FIG. 3 compares the drift stiffnesses for a degree of drift of the tire according to the invention of dimension 195/65 R 15 and of a tire of the same dimension having no meridian stiffening ply as a function of the load supported. On the abscissa axis are borne the loads supported by the two tires mounted on the rim of size 6 J 15 (according to ETRTO standards) and inflated to 2.4 bars, the tires according to the invention being mounted on a vehicle so that the meridian stiffening web is located towards the interior of said vehicle. On the ordinate axis is carried the drift rigidity calculated as the value of the transverse thrust exerted by the roadway on the tire for a degree of drift. The curve (A) in solid lines corresponds to the tire according to the invention, the curve (B) in dotted lines corresponds to the tire without meridian stiffening ply. There is clearly a significant increase in the rigidity of drift for a degree of drift with the tire according to the invention, this increase being all the more important that the load is large.

An alternative embodiment, not shown here, consists in applying the principle of the invention to the case of a crown reinforcement of the tire comprising a first working ply radially located between the carcass and a second working ply, said first ply being folded on itself to at least one of its two axial ends to come partially wrap at least one of the ends of the second working ply. In the case where one of the working plies is folded at one of its ends, it is preferable to place the additional meridian stiffening ply on the side of the crown of the tire axially opposite to that comprising folding.

In all the embodiments presented, and to limit the deformations of the crown of the tire at high speed, it is advisable to provide the presence of at least one crown hooping ply composed of reinforcements oriented substantially parallel to each other in accordance with a substantially circumferential direction; preferably, the average number of reinforcements per unit length in the crown region comprising the crown stiffening ply is less than the average number of reinforcements per unit length in the remainder of the crest.

In another variant of the invention, the meridian stiffening ply may be interposed between two of the working plies. Of course, what has been described here should not be considered as limiting and in particular, the crown reinforcement may be composed of a number of sheets greater than two.

Claims (13)

1. Tyre (1) having a preferential fitting direction to a road vehicle and comprising two beads (12), a crown and two side-walls (6) that connects the beads and the crown, the said tyre (1) having a carcass reinforcement (2) extending from one bead to the other and, radially outside this, a crown reinforcement (3), of width equal to Ls, formed by a stack of at least two crown plies (4, 5), each of these crown plies being of width at least equal to Ls and being composed of a plurality of cords or cables arranged parallel to one another along essentially the same direction, the cables being crossed over from one ply to the next, the said tyre (1) also comprising a meridian rigidising ply (8) positioned radially between the carcass reinforcement (2) and the crown reinforcement (3) and formed by a plurality of cords or cables essentially parallel to one another and making relative to the circumferential direction an average angle between 50° and 90°, this ply (8), of width Lr, having a first edge (9) and a second edge (10), the said two edges being located on the same side relative to the equatorial plane of the tyre, the said tyre being characterised in that it comprises marking means to indicate the side of the tyre on which the meridian rigidising ply is positioned, the said marking means serving to position the said ply on the inside relative to the road vehicle when the said tyre is fitted to the said vehicle.
2. Tyre (1) according to Claim 1, characterised in that the width Lr of the meridian rigidising ply (8) is between 15% and 45% of Ls.
3. ' Tyre (1) according to Claim1 or Claim 2, characterised in that the first edge (9) of the meridian rigidising ply (8) is located a distance D1 from the equatorial plane of the tyre between 35% and 50% of Ls, while the second edge (10) is located between the first edge and the equatorial plane of the tyre.
4. Tyre (1) according to any of Claims 1 to 3, characterised in that the mean compression rigidity of the meridian rigidising play (8) in the direction of the cords or cables of the said ply, is greater than 1 Gpa, this rigidity being obtained by multiplying the compression rigidity of a single cord or cable by the number of cords or cables per unit length of the ply.
5. Tyre (1) according to any of Claims 1 to 4, characterised in that the crown reinforcement (3) consists of at least two crown plies (4, 5), each crown ply consisting of a rubber matrix reinforced by a plurality of textile cords or cables arranged parallel to one another along essentially the same direction, the crown rigidising ply (8) being reinforced by metallic wires or cables.
6. Tyre (1) according to any of Claims 1 to 5, characterised in that the second edge of the meridian rigidising ply (8) is located relative to the equatorial plane at a distance D2 greater than one-third of Lr.
7. Tyre (1) according to any of Claims 1 to 6, characterised in that the angle α of the wires or cables of the rigidising ply (8) has the same sign as the angle β1 of the reinforcing elements of the ply (4) of the crown reinforcement (3) in contact with the said rigidising ply.
8. Tyre (1) according to any of Claims 1 to 7, characterised in that the width Lr of the meridian rigidising ply (8) is between 20% and 35% of Ls.
9. Tyre (1) according to any of Claims 1 to 8, characterised in that the average angle α of the wires or cables of the meridian rigidising ply (8) relative to the circumferential direction is between 70° and 90°.
10. Tyre (1) according to any of Claims 1 to 9, characterised in that the crown of the said tyre comprises radially on the outside a tread (31) made from a rubber mix designed to be in contact with the road during rolling, the said tread being able to be divided in the axial direction in two parts, each part of the tread being provided with a pattern of its own formed of relief elements, the tread pattern of that part of the tread located radially outside the crown area comprising the said meridian rigidising ply (8) having a tread rigidity lower than that of the other part of the tread.
11. Tyre (1) according to any of Claims 1 to 10 comprising, in addition, at least one crown hooping ply consisting of reinforcement elements orientated essentially parallel to one another along an essentially circumferentially direction, the average number of reinforcing elements per unit length in the crown area comprising the meridian rigidising ply (8) being smaller than the average number of reinforcing elements per unit length in the remainder of the crown.
12. Method of fitting to a vehicle a group of tyres (1) having asymmetrical structure, each tyre (1) having two beads (12), a crown and two side-walls (6) connecting the beads and the crown, each tyre (1) having a carcass reinforcement (2) that extends from one bead to the other and, radially outside this, a crown reinforcement (3) of width equal to Ls, formed by a stack of at least two crown plies (4, 5), each of these crown plies having widths greater than or equal to Ls and being composed of a plurality of cords or cables arranged parallel to one another along essentially the same direction and being continuous over the full width of the said plies (4, 5), the cables being crossed over from one ply to the next, each tyre having in addition a meridian rigidising ply (8) arranged radially between the carcass reinforcement (2) and the crown reinforcement (3) and formed by a plurality of wires or cables essentially parallel to one another and forming an average angle relative to the circumferential direction between 50° and 90°, the said meridian rigidising ply (8) having a width Lr, measured between a first edge and a second edge of the said ply, which is between 15% and 45% of Ls, the said two edges being located on the same side of the equatorial plane of the tyre, the method according to the invention consisting in fitting four tyres of the type described in such manner that the meridian rigidising ply (8) of each tyre is located on the inside of the vehicle, i.e. between the inside of the vehicle and the equatorial plane of the tyre.
13. Method of fitting to a vehicle a group of tyres according to Claim 12, characterised in that for each tyre (1) the first edge of the meridian rigidising ply (8) is located a distance D1 from the equatorial plane of the tyre which is between 35% and 50% of Ls, and the second edge of the meridian rigidising ply (8) is located between the first edge and the equatorial plane of the said tyre.

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